Hemorrhoids are frequently found both internally and externally, or may occur in multiples, at the same time. Internal swollen blood vessels typically don't cause symptoms and are first diagnosed when they cause bloody stool.
Internal hemorrhoids can be caused by pregnancy, straining to have a bowel movement, constipation, or other conditions that increase the pressure in the veins of the rectum, such as obesity.
Hemorrhoids can be treated in many ways, including treating the pain with numbing ointments that also reduce the size of the blood vessel, a stool softener/dietary changes to decrease constipation, or weight loss. In severe cases, the veins may be scarred to reduce swelling in an outpatient procedure, or they may be surgically treated.